From the ca.1425 Medulla grammatice (MS Stnh A.1.10) 36a/b: Laciuus: gay. The Medulla grammatice is a collection of 15th century Latin-Middle English glossaries. Latin lascivus had good and bad senses. For the former 'wanton, petulant, sportive, playful, frolicsome, frisky' and for the latter 'licentious, lewd, lustful, lascivious'.

Eric Partridge in his A Dictionary of Slang and Unconventional English (in two volumes), Routledge & Kegan Paul, 1961:

Also, gay house ‘brothel’, gay in the arse ‘(Of women) loose’, to lead a gay life ‘to live immorally’, the gay instrument ‘the male member’, gaying it ‘sexual intercourse’.

So, it seems that "gay" has multiple meanings since at least the 15th century, and that some from the last century or more have had to do with sex. So, why all the hubbub over the last 40 years or so with an additional meaning? One can only wonder.

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